Air carrier departure from PHX described non compliance with SID event; alleging tower's instruction to maintain visual separation with parallel runway departure traffic prohibited compliance with SID.

Narrative

I was the pilot flying. We took off on Runway 25R at PHX. Our PDC was the MAXXO1 departure to 7000 FT but we were assigned runway heading by Tower with our takeoff clearance. Just prior to 1000 FT AFL; Tower asked if we had traffic at 10 o'clock in site. It was a light twin that had take off on the parallel Runway 25L previous to us. We acknowledged that we had it in site. Tower told us to maintain visual separation; fly a 240 degree heading and continue at MAXXO1; 'turn outside the traffic' and contact departure. At this point I was behind and below the traffic but was unsure I could climb; accelerate and keep the traffic in site. I elected to play it safe and level off at 3000 FT and maintain 200 KTS to ensure a safe distance from the traffic. The MAXXO1 required marking a 90 degree turn in front of the traffic. I was not comfortable was doing this knowing I could not maintain visual contact. To complicate matters the traffic was not showing on the TCAS even though it was clearly within the parameters. Upon contacting departure they asked what we were doing and we told them we were trying to resume the MAXXO1 but had leveled off to maintain visual contact with the traffic. He told us to turn to a heading of 280 degrees and climb to FL210; a vector away from the traffic. We were given vectors from there. At no time was there any hazard; we ensured that; and we never got close to the light twin. The Captain asked for Tower phone number and contacted them after the flight. They acknowledged it was a new Controller and that the clearance was non-standard. They also agreed there was never a hazard and the the issue was resolved as far as they were concerned.